The present invention generally relates to a magnetic head for use in magnetic recording and reproduction systems, for example, a video tape recorder and the like, and more particularly, to a magnetic head which can be applied to a high coercive tape such as the so-called metal tape, etc., of which coil force HC is more than 1000 Oe.
Generally, for recording video information and the like on a high coersive tape such as a metal tape at a high density, it is necessary to employ a metallic magnetizable material such as sendust alloy (Fe-Al-Si alloy) formed into a configuration to suit to a narrow track width, for example, of 10 to 30.mu.. For the above purpose, the magnetic head therefor generally has a thin inner sendust core sandwiched between outer reinforcing cores. More specifically, the conventional inner sendust core shown, for example, in FIG. 1 is produced through the steps of filling a bonding or brazing material m such as silver alloy or the like into part of a coil winding recess h at the side of a back or rear gap Bg and also into a brazing material filling groove U which are formed in one sendust core block Sa, fitting said one sendust core block Sa onto the other or counterpart sendust core block Sb for brazing or welding therebetween, and subjecting the sendust core blocks Sa and Sb thus combined to a predetermined machining such as slicing or the like so as to obtain core chips of required size. However, the magnetic head which includes the known inner core as in FIG. 1 constituted by brazing together the two sendust core blocks Sa and Sb each made of thin metallic magnetizable material of 10 to 30.mu. in thickness, only at the back gap side Sb thereof, with the coil winding recess h provided at its intermediate portion, has a problem in mechanical strength owing to absence of any junction at its front gap side Fg, this giving rise to a possibility that a positional deviation may take place at said front gap side in the course of the machining or during use. Meanwhile, even if it is attempted to increase the mechanical strength by increasing the region to be occupied by the brazing material m in the coil winding recess h, the output is undesirably reduced due to decrease of the coil winding region in the recess h.
It should be noted here that, in FIG. 1 and other figures referred to hereinbelow, although the edges at the front gap sides of the inner cores and of the magnetic heads constituted thereby, on which magnetic tapes are slidingly moved, are generally shown as squarish or angular for a schematic representation, such edges are, of course, curved into an arcuate configuration for smooth passage of the tapes in the actual products.
In order to overcome the disadvantages as described above, there has conventionally been proposed an arrangement in which the two core blocks are joined together by brazing material disposed at approximately equal intervals on the confronting faces or edges of said core blocks, but such as arrangement as described above, although favorable for maintaining a sufficient mechanical strength, tends to impair the reproduction output characteristics of magnetic head in high frequency region, since the junctions provided in the vicinity of the coil winding recess give rise to magnetic loss with respect to magnetic flux of short wave lengths in the video region.
In another known inner core, it is so arranged that brazing material filling grooves are provided in the first core block at its back gap and front gap sides, and also in a position between the back gap side and front gap side, while a coil winding recess is formed in the central groove after filling the brazing material into said brazing material filling grooves, and then, the first core block is brazed together with the second core block through gap distance defining layers formed on the front and back gap forming surfaces for subsequent machining of the inner core thus prepared into the predetermined shape. By the above known arrangement, although the mechanical strength may be improved owing to the provision of the junction also at the side of the front gap forming surface with respect to the coil winding recess, the magnetic characteristics of the resultant inner core show a marked deterioration at the high frequency region as shown in the dotted curve B in FIG. 8, which is attributable to the fact that the brazing material tends to flow into the diffusion prevention groove and coil winding groove during brazing to form a diffusion layer thereof to a large extent in the core block, thus adversely affecting the magnetic characteristics at the front gap portion.